The present invention relates to a rotating machine that is equipped with coolers in the ventilation passage where a cooling medium flows to cool the machine. In a conventional rotating machine, as described in Japanese application patent laid-open publication Nos. Sho 60-162432 (1985) or Hei 2-70247 (1990), for example, ventilation passages where a cooling medium flows are formed symmetrically about the rotating axis and an axis perpendicular to the rotating axis, and multiple coolers for cooling the cooling medium are arranged symmetrically about an axis perpendicular to the rotating axis and on top of the rotating machine. Besides, each cooler has the same cooling capacity.
In the above stated conventional rotating machine, however, if the heat load increases as the generating capacity increases, a significant temperature difference is created in the cooling medium depending upon the distance from each cooler and local heat is generated inside the machine, particularly in the so-called air gap, which is the gap between the stator core and the rotor core. If local heat is generated in the air gap, uneven thermal elongation is caused in the rotor along the axial direction, and, resultantly, the thermal vibration stroke of the rotor is likely to become excessive.
Increasing the heat exchange capacity of the coolers, that is, increasing the size of the coolers may be a means for solving the above problem. However, while the absolute value of the temperature increase distributed along the axial direction in the air gap and the absolute value of the local heat can be reduced by this means, the temperature increase distributed along the axial direction in the air gap cannot be equalized simply by increasing the heat exchange capacity of the coolers. Besides, the cooling medium is not utilized efficiently in the above solution, because the air gap is additionally cooled even though it is already being cooled sufficiently and requires no further cooling.
The present invention provides a rotating machine where, by equalizing the temperature increase distribution inside the machine, no uneven thermal elongation is caused along the axial direction of the rotor, and, resultantly, the thermal vibration stroke of the rotor will not be excessive.
The basic characteristic of the present invention resides in the fact that a main cooler and a sub cooler are arranged and configured so that at least part of the cooling medium that has been cooled by the main cooler is further cooled by the sub cooler. That is, the cooling medium is cooled twice by the coolers. As a result, it is possible to supply sufficiently cooled cooling medium to the so-called air gap, which is the gap between the stator and the rotor, along the entire axial direction. As a result, because local heat along the axial direction in the air gap can be restricted and the temperature increase distributed along the axial direction in the air gap can be equalized, no uneven thermal elongation is caused along the axial direction of the rotor and the thermal vibration stroke of the rotor will not be excessive.
The sub cooler is smaller in size than the main cooler, that is, it has a smaller cooling capacity. The cooling capacity can be smaller because the sub cooler is used to cool part of the cooling medium that has already been cooled by the main cooler, and this combination provides more efficient cooling. Because the sub cooler is arranged midway in the branch duct from the exhaust side of the fan to the outer side of the stator core, that is, in a smaller space than the space where the main cooler is arranged, it must be small in size for ease of installation. For this reason, when viewing the rotating machine from the outside, it is seen that a larger cooler, which is the main cooler, and a smaller cooler, which is the sub cooler, are arranged in series along the axial direction.